F5 power amplifier - Page 456

merlin2069er · 20th July 2009, 06:30 PM

Quote:

Originally posted by fff0

Do you mind showing where you got them?
Thanks.

Yes, I need one too.

sangram · 21st July 2009, 05:56 PM

Two questions:

1. If I already had 22V transformers lying around that gave me about 31-32VDC, what is the best course of action:

a. Order new ones anyway,

b. Run the amp at full voltage and back off the bias to keep dissipation manageable,

c. Run the amp at full voltage and full bias, and ensure the heatsinking can handle it, or

d. Regulate the supply rails with a pass transistor (not a pun!) and a zener or two.

Thanks for the input. Hope option 2 looks reasonable. I assume I will lose some power this way, and only get 30 watts or so in Class A. I'm actually OK with that. I will be using 1 c/w heatsink for each transistor, these are heavily finned 10" x 5" TO3 heatsinks (so have a blank mounting area running the length of the extrusion).

Four of these heatsinks will be used, I assume the additional 7 watts of dissipation will not be problem for them even if I ran the amp full tilt.

I mean to check my temperatures for a few days anyway, but would like to reuse these transformers if possible. They are rated to 10A continuous, are heavily overbuilt, and cost me a pretty penny.

I don't want to use regulated supplies if I can help it. The transistor market in India is guaranteed to throw fakes my way, and I'm not cool with blowing up any expensive devices or speakers.

2. I need a wee bit more gain. About 6-8dB will do it. Am assuming opamps will not cut it (I have some LM4562 laying about), any suggestions? I was hoping to build a small tube preamp for these if I could, but need some pointers (not ready circuits, more like a primer on tubes and how to set operating points and gain).

bobodioulasso · 21st July 2009, 06:09 PM

The F5 cannot be supplied with more than 25volts.
If your transformers are torroids, you could unwind some of the secondaries

sangram · 21st July 2009, 06:14 PM

So it's either new transformers or a regulated supply, then. These are EI, so unwinding is not going to be possible.

Just what I was hoping to avoid, but maybe unavoidable.

Nelson Pass · 21st July 2009, 07:35 PM

The F5 would ordinarily withstand operating voltages to about
35 volts, although this would probably create thermal limitations.

vdi_nenna · 21st July 2009, 08:09 PM

Just got mine in the mail. These guys are big and heavy!
Don't know if I'll need two! ...but I'm gonna use them both anyway!

sangram · 21st July 2009, 08:23 PM

Thank you, Mr. Pass

Just the answer I was hoping for, I assume this would mean backing the bias off a bit would help. With the assumption that each transistor needed to be dissipating around 34 watts, at 32 volts operating voltage I would need to be at about 950mA per transistor to maintain similar dissipation levels, and be content with about 28 watts of total Class A power output.

I hope that this will keep the transistors from going into combustion. 28 watts is sufficient for me.

pro · 21st July 2009, 08:52 PM

Last night I tried to make comparative tests between the Zen V4 and F5, using a very well reviewed 5" full range of Italian production. The timbre of the two is slightly different, due to the high output impedance of the V4 (80 hom), but the thing that left me surprised, is that the soundstage of the F5 is at least 15" higher of the Zen one. Could someone try to explain me, the reason for this?
Both ampli with same cable, pre and cd player.
Thank you.

Nelson Pass · 22nd July 2009, 02:47 AM

Quote:

Originally posted by sangram
I would need to be at about 950mA per transistor to maintain similar dissipation levels, and be content with about 28 watts of total Class A power output.

A 1 amp bias point will give you 32 watts peak.

2Amp * 2Amp * 8ohms = 32 watts peak = 16 watts rms (average)

Babowana · 22nd July 2009, 02:47 AM

Steel mills supply mild steel with their mill specs indicating the yield strength of 235 N/sq.mm even if the test results are actually much higher than this value, e.g. 270 N/sq.mm or greater in most cases. Nevertheless, we apply the yielding exactly at 235 N/sq.mm, considering risk management with respect to "life", "property" and "environment" at sea.

The max. gate-drain voltage of 25V given in the datasheet of 2SJ108 reminds me of the similar feeling as above, but no such heavy risk . . .

Sangram, I believe that you would adjust the voltage rating of filter capacitors adequately.

21st July 2009, 08:09 PM	#4556
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA	Antek Transfos Just got mine in the mail. These guys are big and heavy! Don't know if I'll need two! ...but I'm gonna use them both anyway! __________________ Zen, BOZ, BOZ-J, BLS, B1, Mini-A, Audio Sector NOS DAC, Gain Clone, F5, CAT5 Speaker Cable, DIY Allen Wright ICs, MOX II

21st July 2009, 08:52 PM	#4558
pro diyAudio Member Join Date: Feb 2004 Location: Milano	Last night I tried to make comparative tests between the Zen V4 and F5, using a very well reviewed 5" full range of Italian production. The timbre of the two is slightly different, due to the high output impedance of the V4 (80 hom), but the thing that left me surprised, is that the soundstage of the F5 is at least 15" higher of the Zen one. Could someone try to explain me, the reason for this? Both ampli with same cable, pre and cd player. Thank you. __________________ Michele

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21st July 2009, 05:56 PM	#4552
sangram diyAudio Member Join Date: Sep 2002 Location: India	Two questions: 1. If I already had 22V transformers lying around that gave me about 31-32VDC, what is the best course of action: a. Order new ones anyway, b. Run the amp at full voltage and back off the bias to keep dissipation manageable, c. Run the amp at full voltage and full bias, and ensure the heatsinking can handle it, or d. Regulate the supply rails with a pass transistor (not a pun!) and a zener or two. Thanks for the input. Hope option 2 looks reasonable. I assume I will lose some power this way, and only get 30 watts or so in Class A. I'm actually OK with that. I will be using 1 c/w heatsink for each transistor, these are heavily finned 10" x 5" TO3 heatsinks (so have a blank mounting area running the length of the extrusion). Four of these heatsinks will be used, I assume the additional 7 watts of dissipation will not be problem for them even if I ran the amp full tilt. I mean to check my temperatures for a few days anyway, but would like to reuse these transformers if possible. They are rated to 10A continuous, are heavily overbuilt, and cost me a pretty penny. I don't want to use regulated supplies if I can help it. The transistor market in India is guaranteed to throw fakes my way, and I'm not cool with blowing up any expensive devices or speakers. 2. I need a wee bit more gain. About 6-8dB will do it. Am assuming opamps will not cut it (I have some LM4562 laying about), any suggestions? I was hoping to build a small tube preamp for these if I could, but need some pointers (not ready circuits, more like a primer on tubes and how to set operating points and gain).

21st July 2009, 06:09 PM	#4553
bobodioulasso diyAudio Member Join Date: May 2008 Location: On the moon.	The F5 cannot be supplied with more than 25volts. If your transformers are torroids, you could unwind some of the secondaries

21st July 2009, 06:14 PM	#4554
sangram diyAudio Member Join Date: Sep 2002 Location: India	So it's either new transformers or a regulated supply, then. These are EI, so unwinding is not going to be possible. Just what I was hoping to avoid, but maybe unavoidable.

21st July 2009, 07:35 PM	#4555
Nelson Pass The one and only Join Date: Mar 2001	The F5 would ordinarily withstand operating voltages to about 35 volts, although this would probably create thermal limitations.

21st July 2009, 08:23 PM	#4557
sangram diyAudio Member Join Date: Sep 2002 Location: India	Thank you, Mr. Pass Just the answer I was hoping for, I assume this would mean backing the bias off a bit would help. With the assumption that each transistor needed to be dissipating around 34 watts, at 32 volts operating voltage I would need to be at about 950mA per transistor to maintain similar dissipation levels, and be content with about 28 watts of total Class A power output. I hope that this will keep the transistors from going into combustion. 28 watts is sufficient for me.

22nd July 2009, 02:47 AM	#4560
Babowana Formerly "jh6you". R.I.P. Join Date: Jul 2006	Steel mills supply mild steel with their mill specs indicating the yield strength of 235 N/sq.mm even if the test results are actually much higher than this value, e.g. 270 N/sq.mm or greater in most cases. Nevertheless, we apply the yielding exactly at 235 N/sq.mm, considering risk management with respect to "life", "property" and "environment" at sea. The max. gate-drain voltage of 25V given in the datasheet of 2SJ108 reminds me of the similar feeling as above, but no such heavy risk . . . Sangram, I believe that you would adjust the voltage rating of filter capacitors adequately.

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